Recently, a liquid crystal display device which includes an active matrix substrate has been applied to various uses. The active matrix substrate includes a switching element in each pixel. An active matrix substrate which includes a thin film transistor (TFT) as a switching element is referred to as “TFT substrate”.
The TFT substrate includes a TFT and a pixel electrode provided in each pixel, a gate wire for supplying a gate signal to the TFT, a source wire for supplying a source signal to the TFT. The gate electrode, the source electrode and the drain electrode of the TFT are electrically coupled with the gate wire, the source wire and the pixel electrode, respectively. The TFT, the gate wire and the source wire are covered with an interlayer insulating layer. The pixel electrode is provided on the interlayer insulating layer and is coupled with the drain electrode of the TFT in a contact hole formed in the interlayer insulating layer.
As the interlayer insulating layer, an insulating layer which is made of an organic insulating material (hereinafter, referred to as “organic insulating layer”) is sometimes used. For example, Patent Documents 1 and 2 disclose a TFT substrate which includes an inorganic insulating layer and an organic insulating layer provided on the inorganic insulating layer as interlayer insulating layers covering TFTs and wires.
Organic insulating materials have lower dielectric constants than inorganic insulating materials and are likely to be deposited to a greater thickness. If an interlayer insulating layer which includes a relatively-thick organic insulating layer (e.g., having a thickness of about 1 μm to 3 μm) is formed, when the pixel electrode is arranged such that part of the pixel electrode extends over the gate wire and/or source wire with the interlayer insulating layer interposed therebetween, the parasitic capacitance formed between the pixel electrode and the gate wire and/or source wire can be reduced. Therefore, the pixel electrode can be arranged such that part of the pixel electrode extends over the gate wire and/or source wire and, thus, the pixel aperture ratio can be improved.